1. Field of the Invention
The invention relates to a method and an apparatus for cutting a laminate made of a brittle material and a plastic with a cutting tool. The cutting of thin glass or glass-ceramic/plastic laminates is a preferred application.
2. Prior Art
Laminates made of a brittle material and a plastic are composite workpieces, the component parts of which consist of materials that differ greatly on account of their mechanical and thermal properties.
Plastics customarily used for the production of these laminates are generally mechanically relatively flexible or ductile and have a high thermal expansion of typically 20 to 80 ppm/K and a low softening temperature of typically 120 to 260xc2x0 C.
In contrast to this, brittle materials, such as glass, glass-ceramic or ceramic material, used for the production of the above-mentioned laminates are mechanically brittle and generally have a low thermal expansion and a high softening temperature. The thermal expansion of glass is typically around 3.5 to 11 ppm/K and the softening temperature TG is typically 500 to 750xc2x0 C .
Because of the stated very different physical properties of the two materials, until now no method or apparatus has existed for cutting a laminate comprising a brittle workpiece and a plastic with a cutting tool in one operation. The previously known methods and apparatuses relate only to the cutting of the respectively unprocessed material, but not of the composite.
To mechanically cut an unprocessed brittle material, such as glass for example, the glass surface is scored, for example by means of a diamond cutter or a small cutting wheel or a cutting blade made of hard metal. The surface damage produced in this way then represents a rupture joint of the glass, along which the crack runs in a controlled manner under tensile loading. During scoring of the glass, the normal force exerted on the cutting instrument must not exceed a certain value, dependent on the thickness of the glass. Otherwise, this generally leads to an uncontrolled rupture of the glass (H. Jebsen-Marwedel and R.Brxc3xcckner (editors), Glastechnische Fabrikationsfehler [glass manufacturing defects], Springer-Verlag, Berlin, Heidelberg, N.Y., 1980, page 577 et seq., Chapter 12.7, F. Kerkhof and B. Ganswein, Das xe2x80x9cSchneidenxe2x80x9d des Glases [the xe2x80x9ccuttingxe2x80x9d of glass]).
In addition to conventional mechanical cutting, methods in which the inducement of stresses along the cutting line is produced by thermal means have been known for some time. For example, DE 197 15 537 A1 discloses a method and an apparatus for severing flat workpieces made of brittle material, in which a laser beam is used to induce a thermomechanical stress along a separating line.
Furthermore, cutting the unprocessed brittle.material by means of sand blasting using a mask (JP 06008145 A) or by means of water-jet cutting using an abrasive agent (DE 35 33 340 A1) are known.
In contrast to this, unprocessed plastic films are generally either cut with a shear-action cut, using a shearing action of two sharp-edged hard-metal blades moved against one another, or by using a very sharp cutting knife or cutting wheel.
However, all the methods mentioned above are unsuitable for cutting a laminate of the type mentioned, for example a glass/plastic laminate. It is directly evident that the shear-action cutting of the laminate is possible only when using thin types of glass. However, here too the shear-action cut produced by the shearing action in the thin glass sheet gives rise to uncontrolled brittle cracks transversely to the cutting direction. Although a sharp, scalpel-like cutting knife is capable of severing the plastic film, it is not able to cut through or score the glass. Rather, it would very quickly be blunted on the glass surface.
When cutting with a diamond or a small hard-metal wheel, it is necessary according to the above to keep the loading pressure below a certain limit value to avoid uncontrolled rupture of the glass. The maximum loading pressure of the cutting tool limited in this way is not sufficient, however, to sever the film of the laminate composite reliably. On account of its flexibility, relatively high loading pressures (or normal forces) would be required for severing the plastic film, but for their part would again lead to uncontrolled rupture of the glass.
Because of the foregoing facts, it is not possible with the conventional mechanical cutting methods to cut these laminates in one operation. Alternative methods for cutting these composite pieces have a series of disadvantages.
In the known laser cutting, the apparatus expenditure is significantly greater, on account of the laser and the necessary optical peripherals, resulting in significantly higher costs. Vaporized or even pyrolyzed material may be deposited on the laminate or the optical components.
Water-jet cutting leads to soiling of the surface and to surface defects due to the water and the admixed abrasive agent. Cutting by means of sand blasting likewise leads to soiling of the surface and to surface defects of the laminate. These methods usually entail additional cleaning expenditure.
The introduction of these laminates, such as thin glass/plastic laminates for example, into existing product applications, for example in the display industry as a substitute for thin glass substrates, is facilitated considerably if there is an available cutting method which is as compatible as possible with the conventional cutting techniques, causes low additional costs and, if appropriate, can be implemented in existing glass cutting installations.
An object of the present invention is to provide a method and an apparatus for cutting a laminate made of a brittle material, in particular made of glass, glass-ceramic or ceramic material, and a plastic with a cutting tool, whereby the laminate is to be cut as far as possible in one operation, and at the same time a high cutting accuracy and faithfulness to contours as well as rapid cutting are to be made possible.
It is another object of the invention to design the method and the apparatus in such a way that they are compatible with existing cutting methods, that only low additional costs result and that they can, if appropriate, be implemented in existing cutting installations.
According to the invention, these objects are achieved by a method comprising the steps of:
heating the plastic at least in the vicinity of a predetermined cutting line, thereby lowering the viscosity of the plastic,
placing or engaging a cutting tool onto the plastic side of the laminate and adjusting the loading pressure of the cutting tool on the surface of the laminate,
moving the cutting tool relative to the laminate along the cutting line, with severing of the plastic and simultaneous scoring of the brittle material, thereby inducing a mechanical stress, and
additionally increasing, if appropriate, the mechanical stress along the cutting line to exceed the rupture strength of the scored brittle material.
According to the invention, these objects are also achieved by an apparatus comprising
means for heating the plastic at least in the vicinity of a predetermined cutting line, thereby lowering the viscosity of the plastic,
a cutting tool engageable with the plastic side of the laminate with an adjustable loading pressure of the cutting tool on the surface of the laminate,
means for producing a relative movement between cutting tool and laminate along the cutting line, for the purpose of severing the plastic and simultaneously scoring the brittle material, thereby inducing a mechanical stress, and
means for additionally increasing the mechanical stress along the cutting line to beyond the rupture strength of the scored brittle material, if appropriate.
The measures according to the invention make it advantageously possible to cut a laminate made of a brittle material and a plastic, in particular a laminate made of a brittle material laminated on one side with plastic, with a single cutting tool in one operation.
This is advantageous since the use of two cutting tools guided towards each other or one after the other always necessitates complicated and process-sensitive adjustment work, which is not needed in the case of the present solution.
The cutting tool must be guided on the plastic side of the laminate in order to sever the plastic reliably, and at the same time be able to score the brittle material for a brittle fracture at the cutting point.
To solve the fundamental problems mentioned at the beginning in the mechanical cutting of these laminates, it is necessary to lower the high loading pressure of the cutting tool for severing the plastic. By heating-up the plastic at least in the region of a predetermined cutting line, its viscosity is considerably lowered, and a small loading pressure of the cutting tool is already sufficient to sever the plastic.
The possibly required additional increase in the mechanical stress along the cutting line up to the rupture strength of the scored brittle material can be carried out, for example, by bending in the region of the score, a stress-induced crack propagation taking place along the cutting line.
To cut a laminate made of a brittle material laminated on both sides with plastic, the plastic on each side of the laminate is severed and the brittle material is scored either on one side or on two sides.
The severing of the plastic and the scoring of the brittle material may in this case be performed in a single method step with two oppositely arranged cutting tools or in two successive method steps with at least one cutting tool. For this purpose, the plastic is heated up at least in the region of the predetermined cutting line, thereby lowering the viscosity of the plastic, the heating-up taking place at least on the plastic side of the laminate on which the cutting tool is being placed at the time. The cutting tool is placed on one plastic side of the laminate, the loading pressure of the cutting tool on the surface of the laminate being adjustable. A relative movement between cutting tool and laminate is produced along the cutting line, with severing of the plastic on this side.
On the opposite plastic side of the laminate, the cutting tool or a further, additional cutting tool is placed, the loading pressure of the cutting tool on the surface of the laminate being adjustable. A relative movement between cutting tool and laminate is produced along the cutting line, with severing of the plastic and simultaneous scoring of the brittle material, thereby inducing a mechanical stress. If appropriate, the mechanical stress along the cutting line is additionally increased to beyond the rupture strength of the scored brittle material.
The cutting of the laminate made of a brittle material laminated on both sides with plastic, in which the severing of the plastic and the scoring of the brittle material is performed with two oppositely arranged cutting tools. The method according to the invention for cutting this laminate preferably includes the following method steps:
heating-up the plastic at least in the region of the predetermined cutting line, thereby lowering the viscosity of the plastic,
placing a respective cutting tool onto each plastic side of the laminate, the loading pressure of the respective cutting tool on the surface of the laminate being adjustable,
producing a relative movement between the cutting is tools and the laminate along the cutting line, with severing of the plastic and simultaneous scoring of the brittle material, thereby inducing a mechanical stress, the brittle material being scored on one side or on both sides, and
additionally increasing the mechanical stress along the cutting line to beyond the rupture strength of the scored brittle material if appropriate.
In this case, the two cutting tools are preferably arranged directly oppositely and execute a synchronized movement in relation to the laminate along the cutting line.
If the two cutting tools are arranged with a lead with respect to one another, the cutting tool which severs only the plastic on one side of the laminate is preferably arranged leading the opposite cutting tool, which severs the plastic and at the same time scores the brittle material.
The plastic is preferably heated up by radiation, in particular infrared and/or laser radiation and/or by a hot-gas jet. In this case, it is also possible for the entire laminate to be heated up.
The heating-up of the plastic may also be performed, however, by the heated cutting tool, in particular by its heated lower end. In this case, the heating-up of the plastic can be performed both by means of heat energy transfer alone, through the hot cutting tool, at least in the region of the cutting line, and also in addition to the heating-up mentioned.
The heating-up of the plastic may be performed both beyond its softening temperature and below its softening temperature, preferably just below its softening temperature.
By producing a relative movement between cutting tool and laminate, thereby moving the cutting tool and/or moving the laminate along the predetermined cutting line, the heated-up plastic is severed.
Furthermore, the surface of the brittle material can be scored by the cutting tool, and a rupture joint produced, in the same operation. Since the plastic side of the composite has then already been severed, the separating of the laminatexe2x80x94by a tensile stress-induced crack propagation along the rupture joint of the brittle materialxe2x80x94is ensured. The cutting speeds which can be achieved in this case for the cutting-through of the plastic and the simultaneous scoring of the brittle material are comparable with those of conventional glass cutting.
The melted plastic film at the cutting point additionally makes it possible to dispense with the wet film, of water, glycol or propanol for example, often used in conventional glass cutting for improving the cutting quality and for increasing the edge life of the cutting tool.
A fine cut, suitable for severing the plastic and at the same time scoring the brittle material, is preferably obtained by cutting the laminate with a cutting tool having a mounted diamond tip, with a cutting wheel or with a cutting blade.
Diamond, as the hardest mineral, is ideally suited for cutting the laminate, on account of this outstanding property, mounted in the cutting tool, irrespective of whether the natural or artificially cut edges take effect.
Cutting wheels and/or cutting blades that consist of a particularly hard and tough alloy or of a ceramic, in particular of a tungsten-carbide and/or diamond-containing sintered metal, are preferably used. The cutting wheels are preferably tapered in a wedge-shaped manner and provided on the outer edge with highly polished facets.
By inducing vibration, the cutting tool, and particularly its lower end, can be made to undergo axial and possibly also transverse vibrations of low amplitude and adjustable frequency. The cutting is improved as a result. An improvement in the cutting action is not dependent on a particular frequency. However, it has been found that higher frequencies have a better effect as a result of the higher number of vibrations per unit of time. The application of ultrasound is preferred, the high frequency of which can be generated by relatively inexpensive means. Frequencies in the range above 100 kHz can be generated with the required amplitudes only with relatively great expenditure. For producing the ultrasound, a modulator is preferably used, for example an oscillator crystal, or a magnetostrictive modulator, for example a nickel rod introduced into a strong magnetic alternating field. The ultrasound produced by ultrasonic stimulation is understood to mean sound waves at frequencies higher than 16 kHz. According to the invention, sound waves at a frequency of from 20 kHz to 100 kHz and an amplitude of from 5 xcexcm to 40 xcexcm are preferably used. In this case, vibrations of the cutting tool executed longitudinally and/or transversely with respect to the cutting direction bring about a better material displacement of the plastic away from the rupture joint. In this way, renewed flowing together of the just severed, still soft plastic is prevented. The axial vibrations of the cutting tool lower the thrust and bearing forces required for cutting through the plastic and at the same time scoring the brittle material.
The measures according to the invention enhance the cutting quality and reduce the risk of an uncontrolled brittle fracture of the brittle material. As a result, they assist the performance of the process and improve the achievable yield in the cutting operation or make the operation possible in the first place.
The method and the apparatus are suitable with preference for cutting laminates, in particular thin laminates, made of a brittle material, for example of a glass, glass-ceramic or ceramic sheet, and of a plastic, in particular of a plastic film, it being possible for the plastic film to be a scratch-protective film, preferably a scratch-protective film of polyethylene, or of a sprayed-on polymer film.
In principle, the method and the apparatus are suitable for cutting laminates made of a brittle material and a plastic, the viscosity of which can be lowered by means of heating-up by the cutting tool. Suitable plastics are, for example, thermoplastics, and those particularly suited are, for example, polyamides, polycarbonates, polyether sulfones, olefin copolymers, polyethylene-naphthalenes, polyarylates, polypentadienes or polyethylene terephthalate (PET).
The laminates preferably have in this case a thickness of the plastic of from 1 xcexcm to 300 xcexcm and of the brittle material of from 10 xcexcm to 300 xcexcm.
The brittle material and the plastic are preferably bonded to one another by means of a layer of adhesive, the layer of adhesive preferably having a is thickness of from 2 xcexcm to 50 xcexcm.
Alternatively, the plastic may be applied to the brittle material by extrusion, by a casting, spraying or roller-coating method or by laminating on a plastic film.
The method and the apparatus are also suitable, however, for cutting laminates made of a relatively thick brittle material, for example of glass, in particular flat glass, glass-ceramic or ceramic material, and of a plastic, the thickness of the brittle material preferably being up to 30 mm.
Furthermore, laminates of the type mentioned in which the brittle material consists for example of silicon, germanium or carbon can also be cut.
The production of a satisfactory cut line and, in particular, of a satisfactory score path requires a particular arrangement of the cutting tool. The angle between the longitudinal axis of the cutting tool and the cutting plane in the cutting direction is preferably adjustable in the range from 55xc2x0 to 75xc2x0. It is particularly preferred for the angle to be 65xc2x0.